This package provides efficient alternating sequences based on
finger trees. These can represent sequences made up of two types of
element, `e` and `a` where two of the same type of element cannot
follow each other directly.
Four different flavours are provided, isomorphic to `([(a, e)], a)`,
`([(e, a)], e)`, `[(a, e)]`, and `[(e, a)]`.
Cons-like operations are *O(1)* amortised, and append operations are
*O(log(min(n, m)))* amortised.
For more details, please see the Haddock documentation of
Q4C12.TwoFinger.